Prior Art
Numerous paper sheet converting operations require a transitional feed step which entails removal of a single sheet from a magazine stack of sheets, the single sheet being placed in a serial flow production line.
One successful method of accomplishing this transitional step, mechanically, has been to grasp the single, face sheet of the magazine with suction cups secured to an articulated arm mechanism. As the cyclic movement of the arm mechanism positions the suction cups against the magazine face sheet, the cup interiors are selectively opened to a vacuum source. Secure to the suction cups, the arm continues its cycle to draw the single sheet away from the magazine and position it on the serial flow line. Synchronized release of the vacuum releases the sheet from the suction cups.
Although simple in principle and mechanical operation, the subject transitional step can be capricious and unreliable due to a characteristic trait of drawing more than one sheet from the magazine stack. This undesirable trait is normally caused by the air permeability of the sheet. Curiously, the same multiple sheet pick-up malfunction may be triggered by sheet permeability characteristics of opposite extremes. For a highly permeable sheet the powered vacuum at the cups projects through the face sheet and against the second or even third sheet behind the face sheet. In the case of impermeable sheets, resistance to atmospheric penetration through the sheet creates a vacuum behind the face sheet when an attempt is made to draw the face sheet normally from the stack.
Generally, the corrective technique for these symptomatically similar but physically different malfunctions is the same. By one of several devices, the face sheet is required by the suction cups or arm movement to slide into a shorter radius curve or pucker than the second sheet thereby breaking the vacuum between the first and second sheets.
Numerous U.S. patents have issued for mechanical devices of this sort. Representative is U.S. Pat. No. 783,206 issued Feb. 21, 1905 to C. A. Juengst which relies upon two angular bar protrusions from the face of a "sucker-head" to induce a sharply radiused curve in the face sheet of a magazine stack.
Other references of similar disclosure are those of U.S. Pat. No. 2,745, 665 issued May 15, 1956 to H. S. Labombarde and U.S. Pat. No. 3,322,301 issued May 30, 1967 to G. N. Bliss.
While it is presumed that these prior art devices are operative for the purpose disclosed, such devices are cumbersome to attach to or remove from the basic, suction cup arm structure. When the sheet feeder always handles the same paper of exactly the same mechanical characteristics and properties e.g. caliper, basis weight, permeability and stiffness, ease of accessory attachment and removal is of little consequence. However, use of identical sheet properties may be somewhat limiting as to supply sources and productivity.
Paper is a unique material in that the mechanical properties of a particular sheet are intimately related to the machine upon which the paper was laid. Although two sheets from different machines may appear identical as to caliper and surface texture, great differences may exist as to basis weight, permeability and stiffness. A highly calendered sheet may have greater basis weight, less porosity but only slightly greater stiffness for a given caliper thickness.
To the article packaging industry, this scope of paper properties can be both harmful and helpful. If the primary package criteria are caliper, stiffness and printability, a wide range of sources may be available for supply reliability and competitive pricing. However, paper is generally valued by weight. Therefore, higher basis weight paper is more expensive per unit area than lower basis weight material.
For the dominate reasons of supply reliability and continuity, many packaging converters choose to procure their paper from several sources, slight price differentials notwithstanding. Resultantly, the converting machines must be conveniently adjustable to accommodate a running mixture of paper properties.
It is therefore, an objective of this invention to provide suction feed accessories for quickly and conveniently adjusting the permeability responsiveness of the machine.
Another object of the invention is to provide permeability adjustment accessories for sheet feeders that require no subframes or other permanent mounting structure.